Question: If $2a + b + 4c = -3$ and $4x + 8y + 4z = 9$, what is $-7b - 28z - 28x - 14a - 56y - 28c$ ?
Answer: $= -14a - 7b - 28c - 28x - 56y - 28z$ $= (-7) \cdot (2a + b + 4c) + (-7) \cdot (4x + 8y + 4z)$ $= (-7) \cdot (-3) + (-7) \cdot (9)$ $= 21 - 63$ $= -42$